1. Field of the Invention
This invention relates to an improved process for producing chlorotrifluoroethylene, a useful monomer, involving the dechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane at temperatures above 350.degree. C. in the presence of a molecular sieve/copper chloride-alkali metal chloride catalyst.
2. Brief Description of the Prior Art
Polychlorotrifluoroethylene (PCTFE) is a very useful polymer and is employed in the production of thermoplastic copolymers having high impact strength, high solvent resistance and low moisture absorption. The copolymers are utilized in the making of a wide variety of useful industrial articles including chemical piping, gaskets, tank linings, connectors, insulation materials and electronic components.
Since the demand for the polymer is ever increasing, new processes for producing the monomer, chlorotrifluoroethylene (CTFE) are constantly being searched for.
Some commercial processes for producing CTFE involve the dechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane (TCTFE), by using sodium amalgam or zinc dust in alcohol. However, these and other prior art processes employing similar types of dehalogenation reagents, require the use of either dangerous or expensive metal reagents and spent liquors from such processes pose inherent pollution problems.
Two prior art references, U.S. Pat. No. 2,697,124 (1954) and U.S. Pat. No. 3,333,011 (1967, Allied Chemical) describe processes involving dechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane using hydrogen gas. However, these processes possess the disadvantages of requiring a combustible gas, with its attendant hazards, for use in large scale industrial processes for the production of CTFE.
U.S. Pat. No. 2,697,124 (1954) describes a process for dehalogenating fluorochlorocarbons, in the presence of a hydrogen supplying compound, such as ethylene, and a solid catalyst at a temperature of about 100.degree. to about 800.degree. C. Although the process discloses the dechlorination of TCTFE to CTFE, no mention is made of a molecular sieve/copper chloride-alkali metal chloride type of catalyst.
U.S. Pat. No. 3,210,431 (1965) is a related process wherein ethylene is converted to ethylene dichloride by an oxyhydrochlorination reaction. A mixture of ethylene, hydrogen chloride and oxygen is passed over a catalyst comprising copper chloride, didymium chloride, alkali metal chloride and a silica gel carrier at a temperature of about 100.degree. to 300.degree. C. However, the catalyst is not described as being useful at temperatures above 350.degree. C. We have found that normal Deacon-type catalysts do not exhibit a sustained catalyst lifetime in the catalyzed vapor-phase reaction between TCTFE and ethylene in the presence of hydrogen chloride and elemental oxygen at temperatures above 350.degree. C.
U.S. Pat. No. 4,039,596 (1977, Allied Chemical) describes a process for oxyhydrochlorination of C--H containing organic compounds, including methane and ethylene, in the presence of a copper-calcium fluoride catalyst. However, no suggestion is made regarding the utility of the catalyst for dechlorinating compounds such as chlorinated paraffinic hydrocarbons at temperatures above 350.degree. C.
Zeolite-salt occlusion type catalysts are known in the art and representative examples are described in Chem. Phys. Letters, 98,1353-63 (Rabo et al.); J. Chem. Soc. 1958, pp. 299-304 (Barrer and Meier); and Inorg. Chem. 9, No. 6, pp. 1330-1333 (1970, Liquornik and Irvine). However the above references do not discuss or suggest the possibility of forming occlusion complexes of zeolite/copper chloride-alkali metal chloride mixtures for use as catalysts in oxyhydrochlorination processes.
It is known that organic chlorine compounds can be formed from a Deacon-type process, wherein hydrogen chloride is reacted with oxygen to produce chlorine gas in the presence of a catalyst. The in situ formed chlorine is allowed to react with an organic compound such as methane or ethylene to produce a chlorinated product either by a substitution or addition type reaction.
It is also known that organic chlorofluorocarbons can be dechlorinated in the presence of a catalyst by use of an organic chlorine acceptor. The reference, J. Org. Chem., Vol. 36, pp. 3651-53 (1971), describes the use of CTFE as a chlorine acceptor in the dechlorination of CFCl.sub.2 --CFCl.sub.2. However, the reference describes ethylene as being a relatively poor "chlorine sink" in such a chlorine-exchange reaction.
Fellow colleagues of the inventors herein, and having the same assignee, have shown that TCTFE can be dechlorinated to CTFE in the presence of ethylene, by virtue of the fact that chlorine will add to the double bond of ethylene producing ethylene dichloride, EDC. However, in general, the reaction temperature required is usually above 350.degree. C. for good results and the reductive elimination of chlorine from the chlorinated organic compound usually causes carbonaceous products on the catalyst surface which results in reduced catalyst effectiveness.
A very effective catalyst used in the Deacon process is a cupric chloride/potassium chloride eutectic mixture usually used in a form supported on an inert, high surface area substrate such as silica, alumina, titanium and the like. However, at temperatures above 350.degree. C., the active phase of the catalyst will sublime, thus causing a significant decrease in catalyst activity.
We have discovered that a catalyst consisting essentially of an occlusion complex of zeolite/copper chloride-alkali metal chloride eutectic mixture is an effective catalyst at temperatures above 350.degree. C., for dechlorinating 1,1,2-trichloro-1,1,2-trifluoroethane to produce chlorotrifluoroethylene in the presence of ethylene, hydrogen chloride and elemental oxygen, also producing ethylene dichloride as a by-product.